Thermal jacket for battery

ABSTRACT

A thermal jacket adapted to accommodate and cool a storage battery placed in the engine compartment of an automobile and exposed to heat at elevated temperatures emanating from the engine. The walls of the rectangular jacket are formed of rigid, foam-plastic material which thermally isolate the battery from the engine. Embedded in a wall of the jacket is a heat exchanger in which there is circulated a refrigerant fluid derived from the air conditioner installed in the vehicle. The heat exchanger acts to cool the battery to maintain the temperature of the electrolyte therein at a level at which the battery operates at optimal efficiency.

FIELD OF THE INVENTION

This invention relates generally to a storage battery installed in theengine compartment of an automobile where it is exposed to heat at anelevated temperature emanating from the engine, and in particular to athermal jacket for accommodating and cooling the battery to cause it tooperate efficiently.

BACKGROUND OF THE INVENTION AND STATUS OF PRIOR ART

In the typical automobile propelled by an internal combustion engine,there is placed in the engine compartment adjacent the engine arechargeable storage battery. This battery supplies dc power forstarting the car, for energizing the car lights and for powering otherdevices requiring dc power.

Because of the close proximity of the battery to the engine, it isexposed to heat at an elevated temperature emanating from the engine.When the engine has been operating for several hours, the heat of theengine developed during this period and transferred to the storagebattery may impair its operation.

A conventional rechargeable storage battery for an automobile isidentified as a lead-acid battery. The reason for this denomination isthat the electrolyte of the battery is an acid and its plates arelargely formed of a lead-based composition. The positive activeelectrode material of the battery is lead peroxide and the negativeactive electrode material is lead sponge.

When these electrodes are immersed in a sulfuric acid electrolyte(H₂SO₄—H₂O), an electromotive force (EMF) is then developed between theelectrodes. In an auto storage battery, each cell thereof produces anominal voltage of 2 volts. Since the battery must provide a 12 voltoutput, it includes six 2 volt cells connected in a series. However, thevoltage yielded by each storage battery cell is not exactly 2 volts butvaries as a function of the concentration of the sulfuric acidelectrolyte and its temperature.

As noted in the section “Storage Battery” in Vol. 17 page 443 of theMcGraw-Hill Encyclopedia of Science and Technology, when theconcentration of the storage battery electrolyte is 1200 spgr and theelectrolyte temperature is at 25° C. (77° F.), then the cell voltage is2.050V. But when at the same temperature, the acid concentration is 1300spgr, then the output voltage of the cell increases to 2.148V.

Variations in the temperature of the electrolyte give rise to lessdramatic changes in the cell voltage. Thus a small change in thetemperature of the electrolyte produces only a slight change in celloutput voltage in the millivolts range. However, should the electrolytein a battery placed in the engine compartment of an automobile undergo asteep rise in temperature because of intense heat emanating from theengine, then the output of the battery cell may is fall below 2 volts.This results in a drop in the output voltage of the multi-cell batteryso that it is then below its nominal 12 volt value. As a consequence,the battery in this overheated condition may be unable to carry out allof its assigned tasks.

One could try to prevent the electrolyte in a storage battery placed inan engine compartment from overheating by enveloping the battery in athermal jacket composed of thermal insulation material. But in theenvironment of an auto engine compartment, a thermal jacket can onlyfunction to slow down the rate of heat transfer from the engine to thebattery. It cannot prevent a gradual increase in electrolyte temperatureresulting from prolonged operation of the engine in the course of whichthe battery is subjected to heat at high temperature levels.

In the context of a thermal jacket worn by an individual to keep hisbody warm in a cold environment, the jacket then functions to reduce theloss of heat from the body whose temperature is internally regulated sothat it normally is at a temperature of about 37° C. But a storagebattery is not internally heated nor cooled. If, therefore, one wishesto prevent a storage battery in the environment of an automobile enginecompartment from overheating, it then becomes necessary to cool thebattery.

It is known in the prior art to cool the battery of a vehicle to preventit from overheating. Thus U.S. Pat. No. 5,937,664 to Takayoshi et al.(1998) discloses a battery cooling system for a vehicle whose passengercompartment is cooled by an air conditioner. The vehicle battery isplaced in a separate chamber and there cooled by air drawn by a coolingfan from the air-conditioned passenger compartment and blown into thebattery chamber.

The practical drawback to this arrangement is that it makes it necessaryto create a special chamber for the battery as well to provide an aircirculating system between this chamber and the passenger compartment.

SUMMARY OF THE INVENTION

In view of the foregoing, the main object of this invention is toprovide a thermal jacket for an automobile storage battery which acts tocool the battery so as to maintain the temperature of its electrolyte ata level at which the battery operates at optimal efficiency.

More particularly, an object of this invention is to provide a jacket ofthe above type whose walls are formed of closed-cell polyurethane foammaterial having a high degree of thermal resistance whereby transfer ofheat from the battery to the engine compartment and vice versa isminimized, and the temperature of the electrolyte in the battery ismainly regulated by a coolant flowing through the thermal jacket.

Among the advantages of a jacket in accordance with the invention arethe following:

-   -   A. The thermal jacket which accommodates and cools the car        battery does not significantly enlarge the space requirements        for the battery in the engine compartment. Hence no difficulty        is experienced when installing the jacket in the existing space        for the battery.    -   B. The thermal jacket is formed by four walls of synthetic foam        plastic material joined together to create a rectangle, which        rectangle can easily be fabricated at a relatively low cost.    -   C. The jacket incorporates in one of its walls a heat exchanger        through which flows a coolant derived from the existing air        conditioner in the vehicle. Hence this arrangement does not        substantially add to the cost of the installation.    -   D. The thermal jacket improves the performance of the battery        and prolongs its effective life.

Briefly stated, these objects are attained in a thermal jacket adaptedto accommodate and cool the storage battery placed in the enginecompartment of an automobile and exposed to heat at elevatedtemperatures emanating from the engine. The walls of the rectangularjacket are formed of rigid foam plastic material which thermallyinsulate the battery. Embedded in one wall of the jacket is a heatexchanger in which there is circulated a refrigerant fluid derived fromthe air conditioner installed in the vehicle. The heat exchanger acts tocool the battery to maintain the temperature of the electrolyte thereinat a level at which the battery operates at optimal efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention as well as other objects andfeatures thereof, reference is made to the annexed drawings wherein:

FIG. 1 is a top view of a thermal jacket in accordance with theinvention for accommodating an automobile storage battery, the jacketbeing associated with the air-conditioner unit of the auto;

FIG. 2 is a prospective view of the jacket;

FIG. 3 is a separable view of the heat exchanger included in one wall ofthe jacket; and

FIG. 4 shows a jacket arrangement having embedded in one wall thereof athermoelectric device to cool the battery, the device being powered bythe battery.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment: Referring now to FIGS. 1 and 2 of the drawing, showntherein is a standard multi-cell, lead-acid storage battery 10 havingoutput terminals 11 and 12 to provide the 12 volt output required forthe dc powered devices in an automobile. As previously explained, theactual dc output of the battery depends on the existing temperature ofits electrolyte, which temperature may be such as to reduce the outputvoltage.

Battery 10 is installed in the engine compartment of an automobilehaving an internal combustion engine. The concern of the presentinvention is with the heat emanating from the engine which whentransferred to the electrolyte in the battery will overheat it, with aresultant impairment of the efficiency of the battery. Overheating ofthe electrolyte for prolonged periods may also shorten the life of thebattery.

In order to maintain the electrolyte contained in battery 10 in arelatively cool state and thereby cause the battery to function atoptimal efficiency so that its dc output voltage never falls below 12volts, battery 10 is nested within a thermal jacket J whose rectangularstructure is defined by a pair of long side walls 13 and 14 and a pairof shorter end walls 15 and 16. The side walls are bonded or otherwisejoined to the end walls at the corners of the rectangle. The innerdimensions of jacket J substantially match the outer dimensions ofbattery 10. Hence to install the jacket, it is only necessary totelescope it over the battery.

The walls of jacket J are preferably composed of rigid, closed cellpolyurethane foam plastic material having a high degree of thermalresistance and therefore acting as thermal insulation. The use of thismaterial as thermal insulation is well known, as in the thermalinsulation included in refrigerated appliances and vehicles.

Polyurethane resins are produced by the reaction of a disocyanate withat least two active hydrogen atoms, such as diole or diamine. Inpractice, other thermal insulating materials may be used, such as rigidpolyvinyl foam. Embedded in wall 14 of the jacket is a heat exchanger 17formed by a serpentine tube of thermally-conductive material, such ascopper or aluminum. The successive U-shaped branches of the tube lie ina common plane parallel to the planar inner surface in wall 14. The heatexchanger is provided with an inlet 17A to receive a coolant fluid, andan outlet 17B from which the fluid is discharged.

Heat exchanger 17 is associated with a standard air conditioner unit 18installed in the automobile. In a unit of this type, the cooling effecttakes place in an evaporator where heat from the passenger compartmentis absorbed by a low-pressure refrigerant vapor, such as FREON, thevapor being conveyed to a compressor where it is compressed to a hightemperature, high-pressure gas. This gas is fed to a condenser in whichit is condensed to a high-pressure liquid which flows through anexpansion device. In this device it becomes a low-temperature,low-pressure vapor which is fed into the evaporator to complete thecycle. This low-temperature, low-pressure vapor in the first embodimentof the invention functions as the coolant which flows through the tubingof heat exchanger 17 in the thermal jacket J surrounding the storagebattery.

Air conditioner unit 18, by way of a valve 19, is coupled to inlet 17Aand outlet 17B of the heat exchanger 17 whereby the tubing of the heatexchanger is effectively interposed in the fluid line feedinglow-temperature vapor into the evaporator of unit 18. When valve 19 isopen, then the cold vapor from the unit flows through the heat exchangerin the jacket. But when valve 19 is closed, the heat exchanger isdisconnected from the unit.

To thermostatically regulate the temperature of the battery which isbeing cooled by jacket, a heat-sensitive detector 20 is provided whichis mounted in the jacket adjacent its inner surface to yield a signalwhose magnitude depends on the temperature within the jacket.

The signal is conveyed to a thermostatic switch 21 which is arranged toactuate valve 19 when the temperature within the jacket reaches apredetermined level. At this point, valve 19 is opened to admit thecooling fluid into the heat exchanger to cool the battery.

Automatic control of the battery temperature is not essential, unlessone wishes to maintain the temperature of the electrolyte at thattemperature level at which the battery functions at its optimalefficiency. For the battery to function well, it is only necessary toprevent overheating of its electrolyte.

Second Embodiment: In the first embodiment of the invention, it isnecessary to associate the jacket with the air conditioner installed inthe vehicle whose engine compartment contains the battery.

In the embodiment of the jacket shown schematically in FIG. 4, thecooling means is incorporated in one wall of jacket J. It is constitutedby a thermoelectric device of any known type. The typical thermoelectricdevice is formed of two semiconductive devices having dissimilarcharacteristics. These are connected electrically in series and arethermally connected in parallel to create two junctions, one being acold junction and the other a hot junction.

One semiconductor is of the N-type and the other of the P-type. When adc voltage is applied across the dissimilar semiconductors, the junctionconnecting the semiconductors in series to the d-c source becomesintensely cold, whereas the junction thermally connecting the conductorsin parallel becomes hot.

Thermoelectric device 22 which acts to cool the battery derives its dcoperating power from the battery itself. The device is situated in wall14 of the jacket so that its cold junction 22C faces the battery. Heatfrom the hot junction of the device is absorbed by a heat sink (notshown).

To regulate the operation of thermoelectric device 22, the output ofbattery 10 is applied to this device through a thermostatic controlswitch 23. Coupled to this switch is a heat-sensitive detector 24 whichsenses the temperature of the battery within the jacket to produce asignal which activates switch 23 only when the electrolyte temperatureexceeds a predetermined level.

When, therefore, thermoelectric device 22 is turned on by switch 23, itis then powered by battery 10 and serves to cool the battery to preventoverheating of its electrolyte. Thus the battery in effect isself-cooling. In practice, sensor 24 and control switch 23 may beembedded in wall 14 of the jacket, as well as its input terminals to beconnected to the battery.

In the second embodiment, while the power to cool the battery is drawnfrom the battery itself, little power is required for this purpose inthat the battery is thermally insulated from the engine which is thesource of heat, and the volume within the jacket to be cooled is small.

While there has been disclosed preferred embodiments of the invention,it is to be understood that many changes may be made therein withoutdeparting from the spirit of the invention.

1. A thermal jacket adapted to accommodate a storage battery having anacid electrolyte, the battery being installed in the engine compartmentof an automobile and being exposed to heat emanating from the enginewhich may raise the temperature of the electrolyte to a high level atwhich operation of the battery is impaired, said jacket comprising: A. Arectangular structure having an interior dimensioned to accommodate saidbattery, said structure being defined by side and end walls formed ofthermal insulation material which thermally isolate the battery fromheat emanating from the engine; and B. means incorporated in saidstructure to cool the interior thereof to a degree maintaining theelectrolyte of a temperature below said high level.
 2. A jacket as setforth in claim 1, in which the walls thereof are fabricated of rigid,foam-plastic material having a high thermal resistance.
 3. A jacket asset forth in claim 2, in which the foam plastic is closed-cellpolyurethane foam.
 4. A thermal jacket as set forth in claim 1, in whichsaid cooling means includes a heat-exchanger embedded in one of saidwalls through which flows a coolant.
 5. A thermal jacket as set forth inclaim 4, in which said heat exchanger is formed by a serpentine tubeformed by thermally-conductive material.
 6. A jacket as set forth inclaim 5 in which the coolant is derived from an air conditioner unitinstalled in the automobile.
 7. A jacket as set forth in claim 6 furtherincluding a detector to sense the temperature in the interior of thestructure to produce a signal to regulate the flow of coolant in theheat exchanger.
 8. A jacket as set forth in claim 1 in which the coolingmeans is a thermoelectric device incorporated in said structure andhaving a cold junction adjacent said battery.
 9. A jacket as set forthin claim 8 in which dc power for operating said device is derived fromthe battery.